Css style:
Div{width:calc(100%-20px);}
But problem arise here when we use number of tag with calc(). I will change the parent width it automatically adjust but when use a static value in place of percentage. Change every where. Where use calc() method but you forget in one place that will be no affect here but layout will be affected so much. You find the problem and correct it but another alter native solution to defined variable with value. Use variable name to place value so change in one place and affect in all place.I will recommend of that because website layout is relative and no need to defined static height and width
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